About 97 million adults in the United States are overweight or obese. The medical problems caused by overweight and obesity can be serious and often life-threatening, and include diabetes, shortness of breath, gallbladder disease, hypertension, elevated blood cholesterol levels, cancer, arthritis, other orthopedic problems, reflux esophagitis (heartburn), snoring, sleep apnea, menstrual irregularities, infertility and heart trouble. Moreover, obesity and overweight substantially increase the risk of morbidity from hypertension, dyslipidemia, type 2 diabetes, coronary heart disease, stroke, gallbladder disease, osteoarthritis and endometrial, breast, prostate, and colon cancers. Higher body weights are also associated with increases in all-cause mortality. Most or all of these problems are relieved or improved by permanent significant weight loss. Longevity is likewise significantly increased by permanent significant weight loss.
Weight loss treatments vary depending, at least in part, on the degree of weight loss one is attempting to achieve in a subject as well as on the severity of overweight or obesity exhibited by the subject. For example, treatments such as low-fat diet and/or regular exercise are often adequate in cases where a subject is only mildly overweight. Such treatments can be enhanced by controlled use of over-the-counter appetite suppressants including caffeine, ephedrine and phenylpropanolamine (Acutrim®, Dexatrim®). Moreover, prescription medications including amphetamine, diethylpropion (Tenuate®), mazindol (Mazanor®, Sanorex®), phentermine (Fastin®, Ionamin®), phenmetrazine (Preludin®), phendimetrazine (Bontrol®, Plegine®, Adipost®, Dital®, Dyrexan®, Melfiat®, Prelu-2®, Rexigen Forte®), benzphetamine (Didrel®) and fluoxetine (Prozac®) are often used in the treatment of seriously overweight and/or obese subjects or patients. However, such treatments, at best, result in only ˜5-10% weight loss (when accompanied with diet and exercise). Moreover, most of these treatments ultimately prove inadequate because they are either dangerous, ineffective or quickly lose their anorexient effect.
At least one class of these prescription medications, the phentermines (Fastin®, Ionamin®), have been used as monotherapy in the treatment of obesity for about 30 years. The phentermines are members of a class of drugs known as the sympathomimetics for their ability to mimic stimulation of the central nervous system. The phentermines act on the hypothalamus, an appetite control center of the brain. Phentermine monotherapy can increase weight loss when used in combination with diet and exercise, as compared to diet and exercise alone. However, the drug loses effectiveness after about two weeks and, in fact, is not approved by the FDA for use beyond six weeks. Moreover, weight loss may not be permanent, especially after the drug is discontinued. Phentermine treatment is also associated with side effects including nervousness, irritability, headache, sweating, dry-mouth, nausea, and constipation.
In general, available weight loss drugs have limited efficacy and some clinically significant side effects. Studies of the weight loss medications dexfenfluramine (Guy-Grand, B. et al. (1989) Lancet 2:1142-5), orlistat (Davidson, M. H. et al. (1999) JAMA 281:235-42), sibutramine (Bray, G. A. et al. (1999) Obes. Res. 7:189-98), and phentermine (Douglas, A. et al. (1983) Int. J. Obes. 7:591-5) have shown similar effectiveness. Studies for each demonstrated a weight loss of about 5% of body weight for drug compared with placebo. Other serious considerations limit the clinical use of these drugs. Dexfenfluramine was withdrawn from the market because of suspected heart valvulopathy, orlistat is limited by GI side effects, sibutramine can cause hypertension, and phentermine has limited efficacy.
Various combination therapies that include phentermine as one of the agents have been investigated and have met with mixed success. The phentermines were, up until around 1997, often prescribed along with fenfluramine (Pondimin®) or dexfenfluramine (Redux®), nicknamed “fen”, as a combination therapy known as fen-phen. Fenfluramine is a potent releaser of serotonin from serotonergic neurons which acts on a cerebral appetite center. When combined with phentermine, fenfluramine had the effect of enhancing and extending the anorexient action of phentermine. However in 1997, the Food and Drug Administration (“FDA”) asked manufacturers to withdraw Pondimin® and Redux® due to studies which strongly suggested that the drugs cause damage to the mitral valve of the heart and pulmonary hypertension.
More recently, it has been suggested that phentermine in combination with anti depressants is a potentially effective therapy for effecting weight loss, U.S. Pat. No. 5,795,895. In particular, the anti-depressants suggested for use in this new combination therapy are members of a class of compounds known as selective serotonin reuptake inhibitors (SSRIs) which include fluoxetine (Prozac®), sertraline (Zoloft®), fluvoxamine maleate (Luvol®) and trazodone hydrochloride (Desyrel®). The combination therapy is also suggested to treat coexisting depression and/or obsessive-compulsive disorder.
Phentermine has also recently been tested in combination with bupropion (Wellbutrin®) for the treatment of obesity. Bupropion is an antidepressant that inhibits dopamine reuptake, as compared to serotonin uptake. It is also used to treat Attention Deficit Disorder (ADHD), bipolar depression, chronic fatigue syndrome, cocaine addiction, nicotine addiction, and lower back pain. While bupropion alone had a modest effect as a weight loss agent (when prescribed to patients following a 1200 calorie per day diet), patients receiving phentermine in combination with bupropion experienced no greater weight loss than those receiving bupropion alone. Moreover, bupropion use has been associated with drug-induced seizures causing it to be removed from the market by the FDA for at least five years before its re-introduction in 1989.
Accordingly, there exists a need for new, more effective weight loss treatments which are accompanied by fewer adverse or undesirable side effects or less serious side effects. In particular, there exists a need for developing medical weight loss treatments which can potentially lower major endpoints such as death and/or myocardial infarction rates by directly treating obesity rather than treating the consequences of obesity (e.g., diabetes, hypertension, hyperlipidemia), as is currently the practice.